Project Summary The long term goal of this project is to have a better understanding of precisely how the release of the neurotransmitter acetylcholine affects function in a prototypic cortical area of the brain crucially involved in the formation of long term memories. More specifically, we are interested in how the inputs from an area of the brain called the medial septum/diagonal band of Broca, (which releases acetylcholine), affects processing of neural information in an output structure of a cortical area of the brain, (hippocampal CA1), crucial to the formation of long term memories. These studies will have important implications for developing treatments for Alzheimer's disease and possibly schizophrenia. The loss of cholinergic neurons that project to cortical structures in the brain is a hallmark of Alzheimer's disease. Furthermore, drugs that prolong the presence of acetylcholine in the extracellular space are one of the treatments used to alleviate symptoms in Alzheimer's patients. Moreover, dysfunction of neuronal nicotinic receptors has been correlated to some familial forms of schizophrenia. The specific aims for this five year project are to understand how acetylcholine release affects inhibitory interneuron function and ultimately the processing of information in hippocampal CA1. To do this we will express a protein called ChIEF in cholinergic neurons that can excite neurons and its processes when exposed to blue light. This will allow us to elicit the release of acetylcholine in live intact slices of hippocampal CA1 by merely flashing blue light upon them. We will then examine how acetylcholine release through the activation of both nicotinic and muscarinic receptors affects interneuron function and ultimately hippocampal CA1 network function. We will do this by recording electrical responses in interneurons and pyramidal neurons of hippocampal CA1 via whole cell patch clamp methods, and by recording activity in the entire network by using voltage-sensitive dye imaging. The results from these studies will have important implications for the treatment of Alzheimer's disease and some familial forms of schizophrenia.